Add example and type options to attributes

As described; this is used in the nodepool configuration
documentation.

Change-Id: Iad188fd69818762cc9bad927beaff55749e0385c

doc/source/examples.rst

@@ -11,6 +11,8 @@ Configuration Attributes
 
    .. attr:: foo
       :default: bar
+      :example: sample_value_for_example_attr
+      :type: str
 
       A sub attribute.
 

zuul_sphinx/zuul.py

@@ -328,6 +328,8 @@ class ZuulAttrDirective(ZuulObjectDescription):
         'required': lambda x: x,
         'default': lambda x: x,
         'noindex': lambda x: x,
+        'example': lambda x: x,
+        'type': lambda x: x,
     }
 
     def before_content(self):
@@ -361,6 +363,18 @@ class ZuulAttrDirective(ZuulObjectDescription):
             line += nodes.literal(self.options['default'],
                                   self.options['default'])
             signode += line
+        if 'example' in self.options:
+            line = addnodes.desc_signature_line()
+            line += addnodes.desc_type('Example: ', 'Example: ')
+            line += nodes.literal(self.options['example'],
+                                  self.options['example'])
+            signode += line
+        if 'type' in self.options:
+            line = addnodes.desc_signature_line()
+            line += addnodes.desc_type('Type: ', 'Type: ')
+            line += nodes.emphasis(self.options['type'],
+                                   self.options['type'])
+            signode += line
         return sig